Previous abstract Next abstract

Session 105 - Molecular Cores and Protostars.
Display session, Thursday, January 16
Metropolitan Ballroom,

[105.08] Hot H2CO: Observations of Formaldehyde at 650GHz

A. Wootten, J. Mangum (NRAO), M. Barsony (UC-Riverside)

We determine the physical conditions in warm dense cores in molecular clouds via observations of the submillimeter wavelength transitions of formaldehyde (H_2CO). H_2CO is the ideal molecule for this purpose, since its numerous transitions in the submillimeter spectrum allow independent temperature and density determination of the emitting gas. The transitions in the 650 GHz atmospheric window arise from gas which is too warm for depletion onto grains to have hidden it from view. The lowest energy transitions lie at levels 160 K above ground, while the highest energy transitions in the window are the K=8 transitions arising from levels more than 1000 K above the ground state. Since formaldehyde is destroyed at temperatures by chemical reactions at moderate temperatures, little emission is expected from the most highly excited transitions. However, Schilke (private communication) reports the detection of the K=7 transitions at 654 GHz toward IRc2 in OMC1. These lines, which arise from levels 800 K above ground may occur in a transient chemistry, and provide information on conditions in shocked or ablated material quite close to the young star(s) buried in the dense core (Wootten, Loren and Bally 1984 Ap. J. 277, 189). We report observations of several highly excited lines of formaldehyde towards warm HII regions made with the Caltech Submillimeter Telescope (CSO). Our attempt to understand the conditions under which its emission is excited in star-forming molecular clouds confirms that denser, hotter regions give rise to more highly excited submillimeter transitions than heretofore found. In DR21(OH)MM1, for example, densities a factor of four higher than suggested by Mangum and Wootten (1993, Ap. J. Supp. 89, 123) are required to reproduce the strength of the 9_19\rightarrow8_18 transition observed at 632 GHz.

The CSO is operated by the California Institute of Technology under funding from the National Science Foundation, Contract No. AST-93-13929.

If you would like more information about this abstract, please follow the link to This link was provided by the author. When you follow it, you will leave the the Web space for this meeting; to return, you should use the Back button on your browser.

The author(s) of this abstract have provided an email address for comments about the abstract:

Program listing for Thursday